An evo 16g flows ~2lbs per minute more than a b16g. That is a diff of about ~20hp. Here is a bit more info about the turbos:
http://www.dsmstyle.com/forums/showthread.php?t=1229
The thread you pointed to made no claim of a signifigant diff in HP potential. In a car with a s16g and a evo 16g, I would bet on the driver. I do not see a big difference between any of the 16g turbos to justify calling it a worthwile upgrade for you.